U.S. Pat. No. 4,383,172 discloses an apparatus for measuring coating thickness on an elongate continuously moving strip of material, the apparatus utilizing beta backscatter techniques which require that a probe be placed into contact with the strip.
U.S. Pat. No. 4,686,357 disclosed an improved apparatus which can measure the thickness of a coating at a selected measurement site by X-ray technology, wherein the strip of material is not contacted by the measurement device.
In both of the foregoing patents a shuttle is utilized which carries at least a portion of the measurement device, the shuttle being caused to be moved in a direction parallel to the strip by physical engagement with the strip. The foregoing designs are satisfactory when the strip has sufficient strength to pull the shuttle along with the strip without being distorted. However, in recent coating applications the coatings have been applied to very fragile carrier strips or films. In this and some other cases, manufacturers of coated strips have indicated that the strip should not to be used as a direct driving means for pulling the shuttle.